The exosome has emerged as a promising noninvasive biomarker for the early diagnosis of cancer. Therefore, it is highly desirable to develop simple, inexpensive, and user-friendly biosensors for convenient, sensitive, and quantitative exosome assay. Herein, we developed a simple and cost-efficient electrochemical biosensor by combining a metal-organic framework (MOF)-functionalized paper and a screen-printed electrode (SPE) for portable, ultrasensitive, and quantitative determination of cancer-derived exosomes. In principle, the biosensor relied on recognition of the exosome by Zr-MOFs and aptamer to initiate the hybridization chain reaction (HCR) and the formation of DNAzyme for signal amplification. Benefiting from the high signal amplification ability of HCR, the label-free paper-based biosensor is capable of ultrasensitive exosome assay with a detection limit down to 5 × 103 particles/mL, which is superior to that of most reported methods. Moreover, the proposed paper-based biosensor possessed the advantages of low cost, simple operation, and high sensitivity, making it affordable and deliverable for point-of-care (POC) diagnosis in resource-limited settings.

Metal-Organic Framework-Functionalized Paper-Based Electrochemical Biosensor for Ultrasensitive Exosome Assay.

Common homogeneous electrochemical (HEC) sensors usually suffer from the drawbacks of high background signal, low signal-to-noise ratio, and even false positive results due to the preaddition of electroactive substances. Thus, it is necessary to develop novel HEC sensors based on in situ generation of electroactive substances to overcome these shortcomings, which, however, is underexplored. In this work, two-dimensional (2D) nanozymes, i.e., cobalt-doped 2D Ti3C2 MXene nanosheets (CMNSs), with excellent peroxidase-like properties were utilized to develop HEC sensors based on the in situ generation of electroactive substances for organophosphate pesticides (OPs) detection. The 2D CMNSs were synthesized via a template-directed wet chemical approach and displayed outstanding features of hydrophilia and water dispersibility, which could catalyze the oxidation of o-phenylenediamine (OPD) to generate significantly increased reduction current. Interestingly, the 2D CMNSs with peroxidase-like properties exhibited a unique response to thiol compounds and were thus employed as highly efficient catalysts to develop HEC sensors for OPs based on the hydrolysis of acetylthiocholine (ATCh) to form thiocholine catalyzed by acetylcholinesterase (AChE) and the inhibition of AChE activity by OPs. The recovery for OPs analysis of pakchoi extract solutions ranged from 97.4% to 103.3%. The as-proposed HEC sensor based on in situ generation of electroactive substances will provide a new way for the development of high-performance electrochemical sensors and demonstrate potential applicability for the determination of pesticide residues in real samples.

Two-Dimensional Cobalt-Doped Ti3C2 MXene Nanozyme-Mediated Homogeneous Electrochemical Strategy for Pesticides Assay Based on In Situ Generation of Electroactive Substances.

Portable electrochemical biosensor based on laser-induced graphene and MnO2 switch-bridged DNA signal amplification for sensitive detection of pesticide

Breast cancer is very heterogeneous and the most frequently diagnosed cancer worldwide, and precise therapy targeting specific subtypes may improve the survival rates of breast cancer patients. In this study, we designed a biomimetic vesicle by camouflaging catalytic DNA machinery with a breast cancer cell membrane, which enabled the molecular classification of circulating exosomes for subtype-based diagnosis through homotypic recognition. In addition, the vesicles specifically targeted and fused with breast cancer exosomes with phenotypic homology and manipulated the DNA machinery to amplify electrochemical signaling using exosomal RNA as an endogenous trigger. The biomimetic vesicles prepared with MCF-7 cancer cell-derived membranes were shown to recognize estrogen receptor-positive breast cancer exosomes and exhibited a low detection limit of 557 particles mL-1 with microRNA-375 used as the endogenous biomarker. Furthermore, the biomimetic vesicles prepared with MDA-MB-231 cancer cell-derived membranes displayed satisfactory performance in a homotypic analysis of triple-negative breast cancer exosomes with a potential therapeutic target, PD-L1 mRNA, used as the endogenous biomarker. Most importantly, cross-validation experiments confirmed the high accuracy and selectivity of this homotypic recognition-driven analysis for molecular subtyping of breast cancer. When applied to clinical samples of breast cancer patients, the vesicles demonstrated feasibility and reliability for evaluating the molecular features of cancer cell-derived exosomes and enabled stage-specific monitoring of breast cancer patients because the electrochemical signals showed a positive correlation with disease progression. Therefore, this work may provide new ideas for the precise diagnosis and personalized treatment of breast cancer patients throughout the whole disease process.

Molecular Characterization of Exosomes for Subtype-Based Diagnosis of Breast Cancer.

With the continuous development of DNA nanotechnology, various spatial DNA structures and assembly techniques emerge. Hybridization chain reaction (HCR) is a typical example with exciting features and bright prospects in biosensing, which has been intensively investigated in the past decade. In this Spotlight on Applications, we summarize the assembly principles of conventional HCR and some novel forms of linear/nonlinear HCR. With advantages like great assembly kinetics, facile operation, and an enzyme-free and isothermal reaction, these strategies can be integrated with most mainstream reporters (e.g., fluorescence, electrochemistry, and colorimetry) for the ultrasensitive detection of abundant targets. Particularly, we select several representative studies to better illustrate the novel ideas and performances of HCR strategies. Theoretical and practical utilities are confirmed for a range of biosensing applications. In the end, a deep discussion is provided about the challenges and future tasks of this field.

Recent Progress in DNA Hybridization Chain Reaction Strategies for Amplified Biosensing.

Tumor exosomes are promising biomarkers for early cancer diagnosis in a noninvasive manner. However, precise capture and direct analysis of tumor-specific exosomes in complex biological samples are still challenging. Herein, we present a highly efficient dual-aptamer recognition system for precisely isolating and quantifying tumor exosomes from the complex biological environment based on hyperbranched DNA superstructure-facilitated signal amplification and ratiometric dual-signal strategies. When tumor exosomes were captured by the dual-aptamer recognition system, the cholesterol-modified DNA probe was anchored on the surface of the exosomes, activating DNA tetrahedron-based hyperbranched hybridization chain reaction to generate a sandwich complex. Then, the sandwich complex could bind a large number of Ru(NH3)63+ (Ru(III)), leading to a small amount of unbound Ru(III) left in the supernatant after magnetic separation. Hence, the redox reaction between Ru(II) and [Fe(CN)6]3- (Fe(III)) was significantly prevented, causing an obviously enhanced IFe(III)/IRu(III) value. Consequently, highly sensitive detection of tumor exosomes was achieved. The developed approach successfully realized direct isolation and analysis of tumor exosomes in complex sample media and human serum samples as well. More significantly, this ratiometric dual-signal mode and immobilization-free strategy effectively circumvented the systematic errors caused by external factors and the tedious probe immobilization processes, thus displaying the excellent performances of high reliability, improved accuracy, and easy manipulation. Overall, this approach is expected to offer novel ways for nondestructive early cancer diagnosis.

Precise Capture and Direct Quantification of Tumor Exosomes via a Highly Efficient Dual-Aptamer Recognition-Assisted Ratiometric Immobilization-Free Electrochemical Strategy.

A competitive coordination-based immobilization-free electrochemical biosensor for highly sensitive detection of arsenic(v) using a CeO2-DNA nanoprobe.

Portable multi-amplified temperature sensing for tumor exosomes based on MnO2/IR780 nanozyme with high photothermal effect and oxidase-like activity

Antibiotic residues have attracted increasing public attention in food safety because extensive use or misuse of antibiotics seriously threatens public health and safety. Thus, it is important to develop accurate and sensitive analytical methods for the detection of residual antibiotics in foods. Herein, we developed a novel, reliable and highly sensitive photothermal aptasensing platform for analysis of antibiotic residue in food samples. By virtue of CuS/cyanine dye nanocomposite as an excellent photothermal conversion reagent, and dual amplification strategy consisting of exonuclease I-aided target recycling and hybridization chain reaction, highly sensitive detection of antibiotic, i.e . chloramphenicol (CAP), was successfully realized with a detection limit as low as 2.8 pM, which was superior to most of the reported methods for CAP determination. In addition, the as-proposed dual-amplified photothermal aptasensing platform was highly applicable for monitoring antibiotic residue in various food samples with good accuracy and repeatability. More importantly, this work was the first constructed photothermal aptasensing platform for antibiotic detection. Therefore, with the excellent features of simplicity, portability, wide availability, and easy manipulation, this sensing platform has great potential to be applied in antibiotic-related food safety monitoring. A photothermal aptasensing platform for accurate and reliable monitoring of antibiotic residue in foods was established via the dual signal amplification strategy by coupling exonuclease I-assisted target recycling and hybridization chain reaction. • A novel photothermal aptasensing system was constructed for antibiotic assay. • The sensitivity was effectively improved by dual amplification strategy. • The method showed good performance for antibiotic with low LOD and wide linear range. • It was highly applicable for monitoring antibiotic residue in food samples. • It also showed the appealing features of portability, versatility and easy operation. 

Target-activated dual-amplified photothermal aptasensing platform for highly sensitive monitoring antibiotic residue in foods

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Precise Capture and Direct Quantification of Tumor Exosomes via a Highly Efficient Dual-Aptamer Recognition-Assisted Ratiometric Immobilization-Free Electrochemical Strategy.

A competitive coordination-based immobilization-free electrochemical biosensor for highly sensitive detection of arsenic(v) using a CeO2-DNA nanoprobe.

Portable multi-amplified temperature sensing for tumor exosomes based on MnO2/IR780 nanozyme with high photothermal effect and oxidase-like activity

Target-activated dual-amplified photothermal aptasensing platform for highly sensitive monitoring antibiotic residue in foods